Waveguide with reflective grating for localized energy intensity

ABSTRACT

An apparatus includes a waveguide with first and second sections, and a junction coupling the first and second waveguide sections together. The first waveguide section has a first reflective device and the second section comprising a second reflective device arranged to generate a standing wave in the waveguide with maximum energy wave intensity at a target region of the waveguide in response to an incident energy wave being provided into at least one of the waveguide sections.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/321,786, filed on Jul. 1, 2014, which claims the benefit of U.S.Provisional Application Ser. No. 61/951,618 filed on Mar. 12, 2014,which is expressly incorporated by reference herein in its entirety.

BACKGROUND

In magnetic storage devices such as hard disk drives (HDD), read andwrite heads are used to magnetically write and read information to andfrom storage media, such as a magnetic storage disk. An HDD may includea rotary actuator, a suspension mounted on an arm of the rotaryactuator, and a slider bonded to the suspension to form a head gimbalassembly. In a conventional HDD, the slider carries a write head andread head, and radially flies over the surface of the storage media. Themagnetic media disk rotates on an axis, forming a hydrodynamic airbearing between an air bearing surface (ABS) of the slider and thesurface of the magnetic media disk. The thickness of the air bearing atthe location of the transducer is commonly referred to as “flyingheight.”

The read and write heads are mounted on a trailing edge surface of theslider, which is perpendicular to the air bearing surface (ABS). Themagnetic media surface is exposed to the ABS during read and writeoperations. A Heat Assisted Magnetic Recording (HAMR) device or anEnergy Assisted Magnetic Recording (EAMR) device is an enhanced HDD thatapplies heat to magnetically soften the media surface during recording,particularly useful for high capacity storage with physically smallerbit sizes. The heat may be generated by optical energy from a laserdiode coupled to a waveguide, and focused by a near field transducer(NFT) formed on the slider. The NFT is arranged on or near the ABS totransit the focused optical energy to the magnetic media disk surface toproduce the heating.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will now be presented in thedetailed description by way of example, and not by way of limitation,with reference to the accompanying drawings, wherein:

FIG. 1 shows a diagram of an exemplary hard disk drive assembly;

FIG. 2 shows an exemplary waveguide with a reflective mirror to recyclethe incident energy wave;

FIG. 3 shows an exemplary waveguide having a reflective grating;

FIG. 4 shows a detail of an exemplary reflective grating;

FIGS. 5A-5C show various exemplary configurations of waveguides havingreflective grating and/or mirror with single incident wave energy; and

FIGS. 5D-5F show various exemplary configurations of waveguides havingreflective gratings with dual incident wave energy.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various exemplary embodimentsand is not intended to represent the only embodiments that may bepracticed. The detailed description includes specific details for thepurpose of providing a thorough understanding of the embodiments.However, it will be apparent to those skilled in the art that theembodiments may be practiced without these specific details. In someinstances, well-known structures and components are shown in blockdiagram form in order to avoid obscuring the concepts of theembodiments. Acronyms and other descriptive terminology may be usedmerely for convenience and clarity and are not intended to limit thescope of the embodiments.

The various exemplary embodiments illustrated in the drawings may not bedrawn to scale. Rather, the dimensions of the various features may beexpanded or reduced for clarity. In addition, some of the drawings maybe simplified for clarity. Thus, the drawings may not depict all of thecomponents of a given apparatus or method.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiment” ofan apparatus or method does not require that all embodiments include thedescribed components, structure, features, functionality, processes,advantages, benefits, or modes of operation.

Any reference to an element herein using a designation such as “first,”“second,” and so forth does not generally limit the quantity or order ofthose elements. Rather, these designations are used herein as aconvenient method of distinguishing between two or more elements orinstances of an element. Thus, a reference to first and second elementsdoes not mean that only two elements can be employed, or that the firstelement must precede the second element.

As used herein, the terms “comprises”, “comprising,”, “includes” and/or“including”, when used herein, specify the presence of the statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

In the following detailed description, various aspects of the presentinvention will be presented in the context an optical or dielectricwaveguide used to assist magnetic recording on a hard disk drive (HDD).However, those skilled in the art will realize that these aspects may beextended to any suitable application where waveguides are implemented.For example, resonant electromagnetic wave energy in a waveguide antennamay be optimized according to the methods described herein. While theenergy source presented in the following detailed description relates tolight from a laser, those skilled in the art will also realize that thedescribed aspects may be extended to other forms of energy orelectromagnetic waves propagated in a dielectric waveguide. Accordingly,any reference to a waveguide as part of an HDD is intended only toillustrate the various aspects of the present invention, with theunderstanding that such aspects may have a wide range of applications.

Aspects of a waveguide include first and second sections, and a junctioncoupling the first and second waveguide sections together. The firstwaveguide section has a first reflective device and the second sectionhas a second reflective device arranged to generate a standing wave inthe waveguide with maximum energy wave intensity at a target region ofthe waveguide in response to an incident energy wave being provided intoat least one of the waveguide sections.

Aspects of a heat assisted magnetic recording (HAMR) apparatus include awaveguide having a cladding and a core, a near field transducer, and anenergy source arranged to propagate light through the waveguide to thenear field transducer. The core has a plurality of protrusions extendinginto the cladding.

Aspects of a magnetic hard disk drive include a rotatable magneticrecording disk, a slider having a heat assisted magnetic recording(HAMR) device with a near field transducer (NFT), and a waveguide havingfirst and second sections. A waveguide junction couples the first andsecond waveguide sections together. The first waveguide section has afirst reflective device and the second section has a second reflectivedevice arranged to generate a standing wave in the waveguide withmaximum energy wave intensity at a target region of the waveguide inresponse to an incident energy wave being provided into at least one ofthe waveguide sections. The NFT is arranged adjacent to the waveguide atthe target region. The NFT is configured to couple the energy wave tothe surface of the recording disk for heat assisted magnetic recording.

Aspects of a magnetic hard disk drive include a rotatable magneticrecording disk, a slider having a heat assisted magnetic recording(HAMR) device with a near field transducer (NFT), a waveguide includinga cladding and a core, the core having a plurality of protrusionsextending into the cladding, and an energy source arranged to propagatelight through the waveguide to the near field transducer. The NFT isarranged adjacent to the waveguide and configured to couple the light tothe surface of the recording disk for heat assisted magnetic recording.

FIG. 1 shows a hard disk drive 111 including a disk drive base 114, atleast one disk 113 (such as a magnetic disk, magneto-optical disk, oroptical disk), a spindle motor 116 attached to the base 114 for rotatingthe disk 113. The spindle motor 116 typically includes a rotating hub onwhich disks are mounted and clamped, a magnet attached to the hub, and astator. Rotation of the spindle motor hub results in rotation of themounted disks 113. At least one actuator arm 115 supports at least onehead gimbal assembly (HGA) 112 that includes the slider with writing andreading heads. For an EAMR/HAMR enhanced drive, a waveguide and nearfield transducer are included on the slider as well. During a recordingoperation of the disk drive 111, the actuator arm 115 rotates at thepivot 117 to position the HGA 112 to a desired information track on thedisk 113.

FIG. 2 shows a waveguide 101 configured to receive an energy wavegenerated by an energy source 103, and may naturally guide the energywave (e.g., light) to a Near Field Transducer (NFT) 102 arrangedadjacent to the waveguide 101. The waveguide 101 and NFT 102 may bedisposed on a slider of the HGA 112 shown in FIG. 1. As an example, foran optical energy wave, the energy source 103 may be a laser diode. TheNFT 102 may be a passive type NFT which receives energy from the energysource 103 and couples and transfers the energy to the surface of thestorage disk 113. For example, the NFT 102 may focus the energy wavefrom the waveguide 101 to generate a heating spot on the magneticstorage disk 113 to magnetically soften the layers of the disk 113 at anano-sized spot to assist changing the bit state when writing to thestorage disk 113. As a passive NFT, the NFT 102 may operate by a plasmoneffect as optical energy interacts with a small plasmonic metal feature,such as the plasmonic disk 107. Alternatively, the small plasmonic metalfeature may be configured as pin or a ridge, for example. The plasmonicmetal may be one of gold (Au), silver (Ag), copper (Cu), or aluminum(Al) for example. The NFT 102 may be an antenna type NFT as shown inFIG. 2. Alternatively, the NFT 102 may be an aperture type, whichutilizes a nano-sized aperture to confine an input optical energy field.

The waveguide 101 may have a slanted taper with a width approximatelyequal to or greater than the width of the NFT to guide the energy waveto a small area for interaction with the NFT 102. The waveguide 101 mayinclude a core (e.g., a dielectric material core) and a cladding (e.g.,a silicon dioxide material). As shown in FIG. 2, the waveguide 101 maybe configured with two substantially linear sections, a first sectionwhich receives the incident energy, and a second section which includesthe reflective device 103 for reflecting the incident energy. Also, thefirst and second sections of the waveguide 101 may be coupled as shownto form an angular junction at an angle between 0 and 180 degrees.

To recycle the energy wave which passes through the waveguide 101, thereflective device 103 may be arranged at the end of the waveguide 101,as shown in FIG. 2, so the reflected energy wave can be coupled to theNFT 102 in addition to the incident energy wave. A forward propagatingwave can interact with a backward propagating wave to form a standingwave along the waveguide 101. One of several constructive interferencepeaks that are formed at a target region of the waveguide, such as atthe junction of the first and second sections for example. The waveguide101 may be configured with a length for the first section and the secondsection such that a maximum interference peak for the energy wave occursexactly at the target region. The NFT 102 may be positioned adjacent tothe target region of the waveguide 101, thus providing an optimizedefficiency of energy interaction with the waveguide 101.

FIG. 3 shows a diagram of an exemplary embodiment of a waveguide 201that is a variation of the waveguide 101 shown in FIG. 2. In addition toa reflective device 203 at the end of the waveguide 201, anotherreflective device 204 is arranged on the incident section of thewaveguide 201. The reflective device 204 may include a grating to renderit functional as a partial reflection mirror, and to further improve therecycling rate of an energy wave within the waveguide 201. The gratingof the reflective device 204 may be a Partially Reflective Grating(PRG). The reflective device 203 may include a gold mirror. Thewaveguide 201 may be configured with a combination of grating dimensionsfor the reflective device 204 and length the waveguide sections toproduce a standing wave pattern with antinodes 205. Reflectance of thereflective device 204, controllable by the grating composition anddimensions, may react with the incident energy wave generated by energysource 201. If the reflectance of the reflective device 204 is highenough, a trapped wave may form the standing wave inside the waveguideas shown by the anti-nodes 205. A maximum energy amplitude of theantinodes 205 may be produced at a target region of the waveguide 201,by the configuration of the reflective device 204 and the dimensions ofthe waveguide 201. For example, the target region of the waveguide maybe the junction of the first and second waveguide sections. The NFT 202may be positioned adjacent to the target region of the waveguide 201 atone of such anti-nodes 205.

FIG. 4 shows a diagram of an exemplary detail of the reflective device204. Waveguide 301 includes a cladding 305 and a core 304. Thereflective device 204 may include a grating 307 on one surface of thewaveguide 301 and an optional reflective mirror 304 opposite to thegrating 307 to collect scattered light. A plane wave may be assumedinside the waveguide if the lateral size is larger compared to theworking wavelength. For a core material assumed to be non-absorptive,the peak intensity of each anti-node can be represented by Equation (1):

$\begin{matrix}{I_{m} = \frac{\left( {1 - R_{1}} \right)\left( {1 + \sqrt{R_{2}}} \right)^{2}}{\left( {1 - \sqrt{R_{1}R_{2}}} \right)^{2}}} & (1)\end{matrix}$where:

R1 is reflectance of the reflective device 204, and

R2 is the reflectance of the reflective device 303.

Assuming a practically achievable reflectance R2 that varies from 0 to90%, reflectance of the R1 for reflective device 204 may be tunable tomaximize the peak intensity. As an example, reflective device 204 may beconfigured with a reflectance R1=60%, where reflective device 303 has areflectance R2=90%.

In another embodiment, the reflective device 204 may be configured as aretro-reflecting grating 307 and the mirror 306 configured to collectscattered light. The reflectance R1 of reflective device 204 may betuned by the grating parameters such as grating pitch, grating depth,grating duty cycle and overall size of the grating area. The reflectivedevice 303 may be configured as a mirror with a thin gold layer and witha reflectance greater than 90%. The grating 307 may have a 250 nm pitch,grating depth of 90 nm, and duty cycle of 50% for an assumed workingwavelength of 836 nm, and a core material that is Ta₂O₅ with refractiveindex of 2.1. For the cladding material 305 in this example, Al₂O₃ withrefractive index of 1.65 may be used. The core 304 dimensions may be 150nm thickness and 300 nm width for example. The reflectance andtransmission of this grating 307 can be tuned by the overall size ofgrating area or the total number of grating pairs, with a grating pairdefined as a single “grate” unit (i.e., one peak and one valley).

The length of core 304 may be configured to render the resonance of theenergy wave inside the waveguide. As an example, a waveguide maygenerate a resonance having peak intensity at an antinode 205 using acore length of approximately 2300 nm for a core width 300 nm and corethickness 150 nm and grating configured with pitch of 250 nm, gratingdepth of 90 nm and 40 grating pairs.

The waveguide may be configured with a grating size (i.e., number ofgrating pairs) based on estimating a loss for each trip of incident andreflective energy wave interaction with the grating, thus determiningthe optimal number of grating pairs to maximize the intra-cavityintensity.

FIGS. 5A-5F show additional exemplary embodiments of waveguides havingvariations for the reflective devices 203, 204 as shown in FIG. 3.

The waveguides shown in FIGS. 5A-5C are configured in an angularconfiguration similar to the waveguide 201 shown in FIG. 3, with a firstsection of the waveguide that receives the injected incident energy waveand a second section of the waveguide for reflecting the energy wave toform a standing wave.

FIG. 5A shows an exemplary embodiment of a waveguide configured with agrating 501 and a grating 502, both of which may be configured as anetched grating with the core partially etched away and filled with acladding material. Grating 501 may be a partially reflective grating andgrating 502 may be a highly reflective grating.

FIG. 5B shows an exemplary embodiment of a waveguide configured with amirror 503 in the first waveguide section and a grating 504 in thesecond waveguide section The mirror 503 may be formed by a thin Au filmwith a reflectance that may be tuned by altering the thickness of the Aufilm. The mirror 503 may function as a partially reflective mirror. Thegrating 504 may be configured as a highly reflective grating.

FIG. 5C shows an exemplary embodiment of a waveguide configured with twomirrors, the mirror 507 being partially reflective, and the mirror 508being highly reflective.

The exemplary waveguide embodiments shown in FIGS. 5D-5F are suitablefor dual incident energy wave injection, as shown by incident energywave input into each of the two waveguide sections. With such aconfiguration, a mirror with Au film, such as mirror 503 as shown inFIG. 5B and mirrors 504, 505 as shown in FIG. 5C, is eliminated.

FIG. 5D shows an exemplary embodiment of a waveguide configured withetched gratings 507 and 508, which may be formed by etching thewaveguide core material and lining etched surfaces with a reflectivefilm.

FIGS. 5E and 5F show exemplary embodiments of waveguides that are formedwith Width Varying Grating (WVG). As such, the grating 509 and thegrating 510 shown in FIG. 5E, and the gratings 511, 512 shown in FIG. 5Fmaintain the full waveguide interior core dimensions to reduce energyloss for the incident wave and the reflected wave in each section of thewaveguide. Along each of gratings 509-512, the cross-sectional area ofthe waveguide interior is not diminished compared to the cross-sectionalarea of the waveguide interior elsewhere. The gratings 509-512 for theconfigurations shown in FIGS. 5E and 5F are constructed by extending thewaveguide exterior to form the grating pairs, contrasted with the etchedgratings 507 and 508 described above with respect to FIG. 5D. As shownin FIG. 5E, the gratings 509, 510 may be configured as square-shapedextensions of the waveguide width. As shown in FIG. 5F, the gratings511, 512 may be configured as curve-shaped extensions of the waveguidewidth. The external gratings 509-512 may be formed by extensions of thecore material as protrusions into the cladding material of thewaveguide.

The various aspects of this disclosure are provided to enable one ofordinary skill in the art to practice the present invention. Variousmodifications to exemplary embodiments presented throughout thisdisclosure will be readily apparent to those skilled in the art, and theconcepts disclosed herein may be extended to other devices. Thus, theclaims are not intended to be limited to the various aspects of thisdisclosure, but are to be accorded the full scope consistent with thelanguage of the claims. All structural and functional equivalents to thevarious components of the exemplary embodiments described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. §112(f)unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

What is claimed is:
 1. A heat assisted magnetic recording (HAMR)apparatus, comprising: a waveguide comprising a cladding and a core, thecore having a plurality of protrusions extending into the cladding; anear field transducer; an energy source arranged to propagate lightthrough the waveguide to the near field transducer, and wherein thewaveguide comprises first and second sections coupled together at ajunction and wherein the waveguide is configured to optimize anormalized peak intensity of the light at a target region of thewaveguide.
 2. The apparatus of claim 1, wherein the plurality ofprotrusions are square-shaped.
 3. The apparatus of claim 1, wherein theplurality of protrusions are curve-shaped.
 4. The apparatus of claim 1,wherein the plurality of protrusions are partially reflective.
 5. Theapparatus of claim 1, wherein at least one of the first and secondsections comprises the plurality of protrusions, wherein the waveguideis configured to have a number of protrusions that optimizes anormalized peak intensity of the light at a target region of thewaveguide.
 6. The apparatus of claim 5, wherein each of the first andsecond sections of the waveguide have a respective portion of theplurality of protrusions, wherein each of the first and second sectionsof the waveguide receive an incident light wave from the energy sourceand a reflected light wave reflected by the plurality of protrusions ofthe opposite waveguide section to produce a standing wave, wherein thestanding wave includes at least one antinode formed at the targetregion.
 7. The apparatus of claim 6, wherein the near field transduceris arranged adjacent to the target region of the waveguide.
 8. Amagnetic hard disk drive, comprising: a rotatable magnetic recordingdisk; a slider comprising a heat assisted magnetic recording (HAMR)device having a near field transducer (NFT); a waveguide comprising acladding and a core, the core having a plurality of protrusionsextending into the cladding; and an energy source arranged to propagatelight through the waveguide to the near field transducer; wherein theNFT is arranged adjacent to the waveguide, the NFT configured to couplethe light to the surface of the recording disk for heat assistedmagnetic recording and wherein the waveguide comprises first and secondsections coupled together at a junction and wherein the waveguide isconfigured to optimize a normalized peak intensity of the light at atarget region of the waveguide.